This invention relates to an intake pipe pressure detecting device for detecting the pressure in the intake pipe of an internal combustion engine.
Conventionally, the pressure in the intake pipe of an internal combustion engine, i.e., in that section of the intake pipe which is on the downstream side of the throttle valve, has been detected by means of a pressure sensor for the purpose of detecting the intake air amount for the internal combustion engine, thereby controlling the fuel supply amount to the engine, etc. The pressure sensor is usually connected through a pressure introducing pipe to the wall of the intake pipe section situated on the downstream side of the throttle valve, the pressure in the intake pipe being introduced into the pressure sensor through the pressure introducing pipe.
The air flow in the intake pipe, in particular in that section of the intake pipe which is on the downstream side of the throttle valve, contains various contaminants, such as blow-by gas and recirculated exhaust gas (EGR gas). If allowed to enter the pressure sensor, these contaminants will adhere to the sensor wall, thereby deteriorating the accuracy and durability of the pressure sensor. In view of this, Japanese Utility Model Laid-Open No. 57-138036 proposes a pressure detecting device in which any contaminants are prevented from entering the pressure sensor by means of a fresh-air introducing path which serves to introduce clean air into the pressure introducing pipe.
In the above-mentioned pressure detecting device proposed, however, clean air is introduced into a pressure introducing pipe which has a small diameter, so that, in order to avoid a pressure rise in the pressure introducing pipe, only a moderate amount of fresh air can be introduced thereto. As a result, the complete prevention of contaminant intrusion cannot be realized with this device.